This invention relates to channel selecting apparatus for use with plural tuning devices and, more particularly, to such apparatus wherein the particular channels to which the respective tuning devices are tuned are determined by channel selecting signals which are produced by a set of adjustable elements which are common to all of the tuning devices.
Electronic tuning devices are known wherein the usual mechanical or electro-mechanical elements which heretofore had been provided for tuning a tuner to a particular frequency or channel are replaced by controllable reactive elements, such as voltage-controlled capacitors, known as varicaps. With such an electronic tuner, control voltages can be selectively supplied to the voltage-controlled capacitor merely by selectively operating appropriate switches. Thus, for a radio receiver, such as an AM or FM receiver, which includes an AM or FM tuner, an individual switch, such as a pushbutton switch, can be provided for each broadcast frequency which is available in a geographical location and to which the AM or FM tuner can be tuned. For a television receiver, the electronic tuner may be provided with pushbutton switches for each broadcast channel in, for example, the VHF band, together with a number of additional pushbutton switches which may be associated with selected UHF channels to which the television receiver can be tuned.
In electronic tuners of the foregoing type, that is, electronic tuners for use in AM, FM or television receivers, an adjustable element, such as a potentiometer or other adjustable resistance, is connected to each pushbutton switch and is settable to derive a control voltage of predetermined magnitude, which control voltage is supplied, when the associated pushbutton switch is operated, to the tuner. For example, for a television receiver, the pushbutton switch which is associated with channel 2 also is associated with an adjustable element which is set to provide a control voltage that, when supplied to the voltage-controlled capacitor included in the tuner, tunes that tuner to channel 2. Similarly, the pushbutton switch which is associated with channel 3 also is associated with an adjustable element which is set to provide a control voltage which, when supplied to the voltage-controlled capacitor included in the tuner, tunes that tuner to channel 3. The remaining pushbutton switches are similarly associated with adjustable elements which are set to provide other control voltages for setting the tuner to other, desired channels.
As is known, video recording devices, such as a video tape recorder (VTR) includes a tuner whereby the VTR can be tuned to a desired broadcast channel for recording. Typically, the VTR, although operable independently of a monitoring television receiver, often may be used with that receiver in order to permit the viewer to determine the particular program, or information, which is being recorded. Once a viewer confirms that the program which is being recorded is a desired program, he may wish to view other broadcast programs while not interfering with the VTR recording operation. Accordingly, in order to provide this feature, both the television receiver and the VTR are provided with separate tuning devices and, moreover, separate controls are provided for these tuning devices. If such tuning devices are electronic tuners of the aforedescribed type, this means that a separate set of channel selector switches is provided for each tuning device and, moreover, a separate set of adjustable elements, such as a separate set of potentiometers, also is provided for each tuning device.
While electronic tuners provide a significant improvement over mechanical or electro-mechanical tuners, both in performance characteristics and in lower cost of manufacture, a substantial portion of the overall cost of the electronic tuner resides in the adjustable elements. Thus, it is desirable to provide a single set of adjustable elements which can be used to produce channel selecting signals both for the electronic tuner in the television receiver and the electronic tuner in the VTR. It is further desired to avoid any limitation on the independent operation of both electronic tuners, even though a single set of adjustable elements is provided therefor. That is, it is desired to enable the electronic tuner included in the television receiver to be tuned to one broadcast channel while the electronic tuner included in the VTR can be tuned to the same or a different broadcast channel for recording.